1. Field of the Invention
The present invention relates generally to high speed data transmission and, more specifically, to circuit apparatus for compensating for different amounts of propagation delay when gathering data from different data sources. Such a high speed data transmission circuit equalizes the delay associated with data sources in general and thereby eliminates the effects of nonuniform transmission conditions.
2. Description of Related Art
High speed data processing circuits of the type suitable for spacecraft operations principally function to gather high rate digital data from several locations. The data is then multiplexed into a single data stream at the same data bit rate. A conventional prior art solution to gathering high rate digital data is to generate control signals and clock pulses in the central system which are then distributed to data sources with the idea that the delay inherent in the propagation path from each particular data source will be small compared to the data bit period. However, the aggregate delay of cable propagation delays, driver, receiver and logic element propagation delays (a function of temperature) inherent in spacecraft systems can exceed several periods of the clock signal at extremely high data rates. The accumulation of these internal delays makes this approach undesirable at high operating frequencies because delay variations can preclude proper formation of a continuous output data stream.
One pulse transmission system shown in U.S. Pat. No. 4,818,995 converts original signals into line coded signals and transmits them after aligning the timings of the blocks receiving side. As shown in this patent, each output of the parallel receiver circuits 5a to 5c is temporarily stored in delay compensation circuits 7a to 7c. By using a reference clock signal the phases of the read-out pulse blocks are made to equal each other. A specific shortcoming of the system disclosed in U.S. Pat. No. 4,818,995 relating to the problem addressed here is that it simply adjusts relative timing between simultaneously received pulses and confines itself to address alignment pulses which are all transmitted from the same transmitter to the same receiver under the same ambient conditions.